Generally, a lightning arrester is installed at an uppermost part of a building to form a discharge path between a thundercloud and the ground to safely flow charges accumulated in the thundercloud to the ground.
When a normal thundercloud approaches the ground, an electric potential difference between the thundercloud and the ground is about one hundred million volts.
In this state, the air in the atmospheric layer functions as a good insulating body to prevent insulation breakdown between the ground and the thundercloud, i.e., lightning. However, the probability of lightning between the thundercloud and the ground is still in existence.
A lightning arrester using an electric field phenomenon (tip effect), in which an electric field is concentrated to a tip part, is referred to as a Franklin rod type.
A theory of a lightning rod using the tip effect is disclosed in Japanese Patent Laid-open Publication No. S62-216197 (Sep. 22, 1987).
The lightning rod using the tip effect uses a natural phenomenon only. Since the lightning rod is operated only when breakdown of an insulation voltage of the air occurs, it is difficult to effectively prevent lightning in the case that the thundercloud has a lightning hazard just before breakdown of an insulation voltage. For this reason, in this field, various types of lightning arresters have been developed to more effectively and safely discharge charges in the thundercloud to the ground to reduce the number of lightning strikes to an object to be protected.
For example, French Patent Laid-open Publication No. 0096655 (May 26, 1983) discloses a lightning arrester including a main electrode (an electrode grounded to the ground to concentrate ground charges using team effect) and an auxiliary electrode for collecting charges distributed in the air around the main electrode to perform a preliminary discharge with the main electrode, thereby causing discharge between the main electrode and the auxiliary electrode. Ion charges (a former trimmer) through the above discharge are discharged in the air to readily form a discharge path between a thundercloud and the main electrode, thereby absorbing charges in the thundercloud.
In addition, an active lightning arrester disclosed in Japanese Patent Laid-open Publication No. S62-216197 includes a collecting electrode for collecting charges in the air generated when a thundercloud approaches and inducing discharge between an auxiliary electrode and a main electrode, and a determination part for charging the charges of the collecting electrode into a condenser to use them as a power source, and determining variation of an amount of the charges generated from the collecting electrode. When the variation is larger than a predetermined variation rate, a conventional high voltage generating circuit switched by supplying the charges charged in the condenser into a reactor is operated to cause discharge between the main electrode and the auxiliary electrode.
However, since the lightning arrester disclosed in the French Patent, among the above conventional lightning arresters, is installed at the uppermost part of a building, a ground electric field induced by a thundercloud is insignificant at the uppermost part of the building. Therefore, when the charges collected by the charges contained in the air are filled to induce discharge, it is difficult to start the discharge due to insufficient charge, and thus, decrease discharge probability.
In addition, since the lightning arrester disclosed in the above Japanese Patent uses a plurality of electronic components, it is likely to decrease reliability. Further, since the lightning arrester is installed at the uppermost part of a building, i.e., where an operator hardly approaches, when any component of the lightning arrester needs to be replaced due to a malfunction, it is difficult for the operator to perform maintenance on the lightning arrester.
Meanwhile, in order to solve the problem, Korean Patent Registration No. 440616, issued to the same applicant as the present invention, CHUNG Young-Ki, discloses a lightning arrester.
As shown in FIG. 1, the lightning arrester disclosed in Korean Patent Registration No. 440616 includes a fixing bar 10 fixed through a fixing member 15 to the uppermost part of a structure to be protected, a main electrode part 18 connected to an upper end of the fixing bar 10, an upper polymer insulator 12 through which the fixing bar 10 passes and coupled with a lower surface of the main electrode 18 in a contact manner, an auxiliary electrode 13 through which an elongated post part 12a of the upper polymer insulator 12 passes and disposed under the main electrode part 18 in a non-contact manner to charge space charges, a lower polymer insulator 19 through which the elongated post part 12a of the upper polymer insulator 12 passes, installed under the lower surface of the auxiliary electrode part 13, and spaced apart from the fixing member 15 to obtain an insulating distance therefrom, an anti-separation disc member 10a having a through-hole through which the fixing bar 10 passes to prevent separation of the lower polymer insulator 19 from the elongated post part 12a of the upper polymer insulator 12, and a nut member 10b having an inner threaded part to be threadedly engaged with one end of the fixing bar 10 to securely fix the anti-separation member 10a. 
The main electrode part 18 functions to directly attract lightning when the lightning occurs due to approach of a thundercloud. For this purpose, the main electrode part 18 includes a disc plate having a center hole through which one end of the fixing bar 10 passes, and a plurality of nibs 18a radially extending from a periphery of the disc plate at predetermined intervals.
The nibs 18a are bent upward when seen after the lightning arrester is installed.
The upper polymer insulator 12 has an elongated hollow post part 12a through which the fixing bar 12 passes, and upper and lower extension flanges 12b and 12c extending from one end of the elongated post part 12a, i.e., an upper periphery of the elongated post part 12a and spaced apart from each other to obtain an insulating distance between the main electrode part 18 and the auxiliary electrode part 13.
The auxiliary electrode part 13 includes: a first electrode member 13a having a through-hole through which the elongated post part 12a passes, and a plurality of projection pins 13e extending upward from a periphery thereof at predetermined intervals, disposed under the lower extension flange 12c of the upper polymer insulator 12, and not in contact with the main electrode part 18, thereby absorbing a larger amount of charges in the air depending on approach of a thundercloud; a pair of second auxiliary electrode members 13b having an upper surface in contact with a lower surface of the first auxiliary electrode member 13a, and a through-hole through which the elongated post part 12a passes; a third auxiliary electrode member 13c having a hollow post shape through which the elongated post part 12a of the upper polymer insulator 12 passes such that the elongated post part 12a projects downward from the third auxiliary electrode member 13c by a predetermined distance, an upper end of which is in contact with a lower surface of the second auxiliary electrode members 13b, and an inner periphery of which is spaced apart from an outer periphery of the elongated post part 12a passed therethrough; and a filler material 13d formed of titanium dioxide filled in the third auxiliary electrode member 13c through the medium of O-rings inserted into both ends thereof to increase a filling amount and prevent leakage of the filler material 13d. 
The lower polymer insulator 19 includes a short post part 19a having a through-hole through which the elongated post part 12a of the upper polymer insulator 12 passes, and upper and lower extension flanges 19b and 19c extending from one end of the short post part 19a, i.e., an upper periphery of the short post part 19a and spaced apart from each other to obtain an insulating distance between the auxiliary electrode part 13 and the fixing member 15.
When a thundercloud approaches the conventional lightning arrester installed at the uppermost part of a building to be protected, the fixing bar 10 and the main electrode part 18 in contact with the upper end of the fixing bar 10 are charged with ground charges, the auxiliary electrode part 13 not in contact with the fixing bar 10 and the main electrode part 18 by the upper polymer insulator 12 is charged with space charges by the filler material 13d formed of titanium dioxide filled between the third auxiliary electrode member 13c and the elongated post part 12a of the upper polymer insulator 12, thereby attracting lightning generated from the thundercloud far from the lightning arrester.
As a result, it is possible to attract lightning and stably discharge the lightning to the ground even at a low voltage due to a far distance of the thundercloud.
However, in the conventional lightning arrester, when the fixing bar 10 and the main electrode part 18, in which ground charges are charged, are spaced a certain distance apart from the auxiliary electrode part 13, in which space charges formed by approach of a thundercloud are charged, discharge performance of the lightning arrester may be decreased, thereby lowering lightning prevention ability.
In addition, Korean Patent Registration No. 433011, issued to the same applicant as the present invention, CHUNG Young-Ki, discloses a lightning arrester.
As shown in FIG. 2, the lightning arrester of Korean Patent Registration No. 433011 includes a fixing bar 20 fixed through a fixing member 29 to the uppermost part of a building to be protected, a cap member 21 fastened to one end of the fixing bar 20, a polymer insulator 22 mounted on an upper end of the fixing bar 20, formed of an electrostatic induction sphere, and through which an upper end of the fixing bar 20 passes to increase an insulating distance between the cap member 21 and an auxiliary discharge member 24 to be described, the auxiliary discharge member 24 having at least one thin plate passing through a lower center of the polymer insulator 22, a preliminary discharge cap member 25 formed of a conductive material and having a through-hole through which the lower end of the polymer insulator 22 passes such that an upper surface of the cap member 25 is in contact with a lower surface of the auxiliary discharge member 24, and a preliminary discharge member 26 fixed to the fixing bar 20 through the medium of a plurality of insulating ring members 27 disposed under the preliminary discharge cap member 25, formed of a circular disc shape, and having a downward projection, a through-hole through which the fixing bar 20 passes, and a fixing hole formed at a periphery of the projection and in communication with the through-hole to fix the preliminary discharge member to a periphery of the fixing bar 20 using a screw.
In addition, a protection member 23 is attached to an upper surface of the auxiliary discharge member 24 to prevent damage of the preliminary discharge member 26 from an external power.